Wide band slot antenna



April 24, 1962 e. ROBERT-PIERRE MARl 3,031,665

WIDE BAND SLOT ANTENNA Filed Dec. 15, 1959 2 SheetsSheet 1 5 4 7 M.) U!- 4 1 w .lr M a y N M B Z W INVENTOR GEORGES ROBERT-PIERRE MAR/ April 24, 1962 G. ROBERT-PIERRE MARl WIDE BAND SLOT ANTENNA 2 Sheets-Sheet 2 Filed Dec. 15, 1959 INVENTOR GEORGES ROBERT-PIERRE MAR/E United rates atent 9 3,031,665 WIDE BAND SLGT ANTENNA Georges Rohert-Eerre Marie, Paris, France, assignor to Societe dApplications Generales dElectricite et de Mecanique, Paris, France, a corporation of France Filed Dec. 15, 1959, Ser. No. 859,683 Claims priority, application France Dec. 20, 1958 6 Claims. (Cl. 343-470) This invention relates to wide band aerials.

It is an object of the invention to provide an aerial adapted to operate correctly on a very wide band of frequencies, the ratio between the extreme frequencies which may be radiated emciently by said aerial reaching a figure as high and exceptional as 10, without any modification in the mechanical structure of the aerial. This result is obtained in accordance with the invention, chiefly by resorting to different methods of radiation applied in succession, without any mechanical change, when operation is shifted from one end of the range of frequencies to the other end.

In order to obtain said result and in accordance with a main feature of my invention, the improved aerial includes primarily two radiating slots coupled in parallel relationship, the edges of said slots forming the points through which the aerial is fed when said aerial operates as a transmitting aerial or energizing points when it perates as a receiving aerial. Furthermore, the two slots are formed on the same conductive panel, including in its middle a central opening which cooperates for low frequencies with the system of two slots, with a view to obtaining at said lower end of the frequency range an efficient radiation.

Furthermore, and in accordance with another feature of my invention, there are provided, in a modification, two pairs of slots formed on the same panel and cooperating with a central cross-shaped opening, so as to form the equivalent of two systems radiating each, independently of each other, waves which are subjected to a rectilinear polaiisation, the directions of polarisation for the two systems being perpendicular to each other.

My invention will be readily understood upon reading of the following description of various embodiments incorporating further features of interest. In said drawings:

FIGS. 1 and 2 illustrate a slotted aerial of a conventional type, wherein the connections have been however improved, with a view to widening the pass-band, said FIGS. 1 and 2 being respectively a plan view and a sectional view of the aerial.

FIGS. 3 and 4 are a plan view and a lateral sectional view of a system of two slotted aerials fed in parallel and positioned on a panel including a central opening of a suitable shape, with a view to increasing the Width of the frequency pass-band in accordance with one of the features of my invention.

FIG. 5 is a perspective view of an aerial associating two radiating systems executed in accordance with my invention.

In said drawings, the same reference numbers designate the same members on the different figures.

I have illustrated in FIGS. 1 and 2 an aerial with a conventional slot constituted mainly by a generally rectangular opening 1 with a constricted section, the edges of which 5 and 6 are located in the central area of the aerial, so as to receive or to collect between them the high frequency voltage which is fed to or tapped off them by a suitable coaxial cable. Said opening or slot 1 is formed in a metal panel 7, say of a rectangular shape, as illustrated.

The connection between the edges of the slot 1 and the 3,93lfifi5 Patented Apr. 2 5:, i952 coaxial cable is obtained, as illustrated in FIG. 2, by connecting the outer sheathing conductor 13 of said coaxial cable with a metal stud 9 connected in its turn through galvanic means 2 with the edge 6 of the slot 1. The inner conductor 8 of the coaxial cable passes through a bore 3 formed in the stud 9 and extends inside a bore 4- formed in a similar stud 10 facing the stud 9, said inner conductor 8 being connected with said stud 10 at the point 11 located at the bottom of its bore. Said stud 10 is not connected directly with the slot edge 5 but only through a polyethylene blade 12, so as to form a condenser of a capacity C, whereby the stud 10 and the edge 5 of the slot are capacitively connected. On the other hand, the portion of the inner conductor of the coaxial cable located inside the bore formed in the stud 10 acts in association with the latter as an induction coil having a value L, so that, from an electrical standpoint, the coaxial cable 813 is connected with the slot through the agency of an inductance and a capacity inserted in series. Of course, the inner section of the inner conductor of the cable extending between the studs 9 and 16 is not surrounded by the outer conductor.

The aerial thus described is generally associated with a reflector constituted by a fiat panel 14 (FIG. 2) located at a suitable distance behind the panel 7, the size of said reflector being larger than that of the first-mentioned panel 7; the horizontally shaded portions shown in FIG. 1 correspond to the outer section of the reflector 114 extending beyond the edges of the panel '7 and to the section of the reflector 14 appearing through the slot. Such a reflecting panel may be executed in the usual manner by means or" a grid or of a system of rods.

The field radiated by said aerial is subjected to a linear polarization, the direction of polarization registering with the line connecting transversely the edges 5 and 6 of the slots.

Assuming the characteristic properties of the different elements and, chiefly, the capacity C and the inductance L are suitably selected, taking into account the size of the slot, it is possible to obtain a satisfactory operation of the aerial within a comparatively wide range of frequencies extending, for instance, between a frequency f and a frequency 3 i.e. in a ratio as between 1 and 3.

For this range of operation, the matching is satisfactory and the rate of the stationary waves does not extend beyond a value of about 2, this being ascribable, in particular, to the parts played by the capacity and the induction coil L.

It is a known fact that it is possible to give the system including the slot and the feeding means a size such that the aerial provides an impedance of the order of ohms across the coaxial cable. However, if it is necessary to reduce the impedance to the order of 50 ohms, which value is preferable for obtaining an efficient operation of the feeders, a number of difliculties arise, which cannot readily be cut out.

These difiiculties may be removed by resorting to a radiating system including two slotted aerials of the type disclosed and by feeding said aerials in parallel, the two coaxial cables of an impedance of 100 ohms being connected in parallel with a common feeder of a matching impedance of 50 ohms, as provided by a conventional T-shaped connection.

It is thus particularly easy to provide an impedance of 50 ohms for the actual feeder, whereas the impedance formed by each slot considered alone is equal to 100 ohms. Furthermore, the gain of such radiating systems executed is substantially twice that of a single slot.

It is apparent that, for high frequencies, the currents induced at the surface of the conductive panel 7 are 3 localised in areas adjacent the edges of the slot; said currents extend gradually their operative area further and further away from the center of the slot when the frequency of the voltage applied across said edges decreases and the disturbances due to the fact that the size of the panel 7 is limited in all directions modify to a gradually increasing extent the value of the impedance formed by the radiating means across the coaxial cable.

When the same metal panel is provided with two identical slots of the type disclosed, and of which the longitudinal axes are parallel, the longest wavelength for which the system thus executed radiates in a satisfactory manner is substantially equal to twice the distance separating the longitudinal axes of the slots. As a matter of fact, for the lower frequencies, the portion of the panel extending between the two slots radiates in the same manner as a half wave aerial energized through both ends, while the impedance applied to the coaxial cable becomes then much higher than the matching impedance of said coaxial cable, which leads to a reflection of the energy and to a poor efficiency.

It may be attempted to increase said upper limit wavelength by increasing the spacing between the two slots, in which case the aerial becomes too bulky and, furthermore, the radiating diagram for the high frequencies of the range shows a series of lateral lobes which are much too large.

In accordance with my invention, I remove both these drawbacks by resorting to a radiating system constituted by a single metal panel or plate 16, as illustrated in FIG. 3 and provided with two identical slots 17 and 18, the longitudinal axes of which are parallel and the spacing between which is comparatively small, while a third slot 21 is formed in the panel 16 in its central area between the two slots 17 and 18, the length of said slot 21 being substantially equal to twice the length of the slots 17 and 18.

Experience shows that the presence of this slot 21 extends remarkably on the low frequency side the range for which the aerial thus executed is correctly matched and radiates efliciently. FIG. 3 is a plan view of such an arrangement, FIG. 4 being a sectional view thereof.

The coaxial cables having a matching impedance equal to 100 ohms and which are connected with the slots 17 and 13 are shown in dot-and-dash lines in FIGS. 3 and 4 with the reference numbers 40 and 41. Of course, the connections between the coaxial cables and the slots are of the type illustrated in FIG. 2. The cables are interconnected by a conventional T-shaped connection 43 With the feeder 42 having a characteristic impedance equal to 50 ohms.

The horizontally shaded portion of FIG. 3 illustrates the sections of the reflecting panel 45 extending beyond the panel 16 or appearing through the slots. Said reflecting panel is shown in cross-section in FIG. 4.

It is also possible, without widening the scope of the invention, as defined in the accompanying claims, to modify the outline of the panel 16, as described hereinafter with reference to FIG. 5.

It is also possible to modify the outline of the central slot 21 without disturbing the operation of the system.

'It is possible, in particular, to give said central slot 21 tion.

Said arrangement is illustrated in FIG. showing a panel 16 of the type illustrated in FIG. 3 and provided with two pairs of operative slots, respectively at 17-18 and 2829 in association with a central cross-shaped 4 opening 27 playing the same part as the slot 21 in the embodiment illustrated in FIG. 3.

The panel 16 is in the shape of a square, the apices of which are located at the points 50, 51, 52, 53, said square including projecting'parts along its sides, in which projections are cut the ends of the cross-shaped slot 27 extending beyond said sides.

The stats 17 and 18 are fed by coaxial cables 40 and 41 connected with a common feeder 42, while the slots 28 and 29 are fed similarly by the coaxial cables 46 and 47 connected in their turn with a second feeder 48.

The slot 27, of which the outline is formed chiefly, as described, by two rectangles having the same center and shifted with reference to each other by retains the same shape when it is shifted angular'lyby one quarter of a revolution. It plays thus the same function with reference to the slots 28 and 29 and with reference to the slots 17 and 18. The reflector associated with the panel alsocarries the reference number 45, as precedingly. in order to make it appear more clearly, the sections of said reflector apparent to view are shown horizontally shaded in FIG. 5. The apparent shifting between the front panel and the reflector is provided by the perspective showing of the two parts.

The reflector is obviously constituted by a metal plate or a grid and the panel 16 is secured thereto through metal tubes or uprights perpendicular to the plane of the panel and located in proximity with the edges of the radiating slots which face away from the center of the panel. These uprights carry the reference numbers 3233 for the slot 17, 3435 for the slot 18, 36-37 for the slot 28 and 38-'39 for the slot 29. They are also shown in perspective view.

As illustrated, the upright 33 is arranged symmetrically of the upright 32 with reference to the transverse axis of the slot -17 which is perpendicular to its longitudinal axis, and the same is the case for the other pairs of uprights. It is preferable, Without this being essential, for the distance between the axes of two adjacent uprights, to be substantially equal to the common length of said uprights, i.e. to the distance separating the planes of the panels -16 and 45. As a matter of fact, when the metal tubes forming said uprights vibrate at half wave frequency and produce an electric short-circuit between the panel 16 and the reflecting panel 45,'they are located at a distance of one quarter wave from the point at which the coaxial cable energizes the cooperating slot and, consequently, the presence of said uprights does not modify the value of the impedance across the coaxial cable.

EXperience shows that the fact of locating the uprights in the manner disclosed allows cutting out the parasitic vibrations which would otherwise appear between the panel 16 and the reflector 45.

On the other hand, a number of uprights serves for the passage therethrough of the coaxial cables connected with the slots.

The distance separating the planes of the panel 16 and of the reflector 45 is selected, so as to obtain a correct matching and a proper radiating diagram for the high frequency section of the radiated range.

Experience shows that towards the lower end of said range, the size of the reflector 45 is not suflicient for obtaining a suitable directional effect for the radiating system.

Now, according to a further feature of the invention the directional effect for the lower frequencies is improved by locating to the rear of the reflector 45 a second reflector, the action of which is limited, in practice, to the lower frequencies. Said second reflector may be constituted very simply by rods such as 26 for the polarisation of the waves radiating by the slots 17 and 18 and by rods perpendicular to the former and which are not illustrated for the waves radiated by the slots 28 and 29.

From a mechanical standpoint, and for sake of an easier transportation, it is of advantage that, except for nervthe rods such as 24- and 25, referred to hereinafter, and as 25, which may be readily of a removable type, the mechanical system including the radiating panel 16 and the reflector does not project outside a geometrical parallelopipedon having for its base the square, the apices of which are designated by 50, 51, 52, 53. To reach this result and in accordance with a still further feature of the invention corresponding to a modified embodiment, the sections of the panel 16 extending beyond said square are advantageously folded back by 90 rearwardly in planes perpendicular to the plane of the front panel. Consequently, a fraction of the two rectangles forming the central slot 27 is also folded back.

Under such conditions, and if the size of the reflector 45 is the same as that of the square having its apices at 50, 51, 52, 53, it is found that there is a mismatching for frequencies such that the length of the diagonal of the square 56, 51, 52, 53 approximates an integral number of half Wavelengths of the radiated waves.

In order to cut out this drawback, and in accordance with a last feature of my invention, the reflector is associated with rods extending along said diagonal beyond its apices. Said rods, illustrated at 24-25 and 39-31, have lengths which are substantially equal to one half that of the diagonal of said square. Their presence clamps the vibrations of the reflector 45 for wavelengths corresponding to a mismatching. As a matter of fact, for such waves, the reflector vibrates at half-wave frequency and shows an impedance, which is infinite, at the apices of the square. The rods such as 24--25 vibrate thus at quarter Wave frequency and show at said apices their own radiating impedance which is of the order of 72 ohms, which cuts out the resonance leading to such a mismatching of the system.

It should finally be remarked that the radiating system thus constituted is generally carried by a metal mast, through the agency of securing means fitted on the reflector panel 45, said securing means being preferably located in an area adjacent the center of said reflector panel.

When a metal mast is resorted to for carrying the aerial, it is possible to cut out the vertical rods such as 26, since the metal mast forms an advantageous substitute therefor.

Experience has shown that an aerial of the type considered, the sides of which measure 1.28 meter, provides at satisfactory radiation of the waves, the frequencies of which range between 90 megacycles and 950 megacycles, the rate of the stationary waves lying for all the frequencies inside said range underneath a value equal to 2.3.

Obviously, many details may be modified in the embodiments disclosed, chiefly as concerns the auxiliary mechanical supports of insulating material which may be incorporated for increasing the mechanical resistance of the system, without unduly widening thereby the scope of the invention as defined in the accompanying claims.

In FIG. 5, the arrows drawn inside the cross-shaped central slot 27 define the structure of the electrical field inside said slot.

What I claim is:

1. An aerial adapted to radiate satisfactorily throughout a very Wide range of frequencies, comprising at least one feeder, a pair of coaxial cables fed by said feeder and a plate provided with at least one pair of symmetrical slots fed by the coaxial cables of the corresponding pair and with a central slot extending symmetrically between the slots of each pair and substantially longer than the latter, and a reflector plate parallel with the slotted plate and lying at a small distance behind the latter.

2. An aerial adapted to radiate satisfactorily throughout a very wide range of frequencies, comprising two feeders, a pair of coaxial cables fed by each feeder and a plate provided with two pairs of symmetrical slots, the slots of said pairs being arranged symmetrically with reference to two perpendicular axes drawn on said plate, the slots of each pair being fed by the coaxial cables of the corresponding pair and the plate being further pr vided with a central cross-shaped slot, the arms of which are equal and symmetrical and extend along the bisecting lines of said perpendicular axes.

3. An aerial adapted to radiate satisfactorily throughout a very Wide range of frequencies, comprising two feeders, a pair of coaxial cables fed by each feeder and a plate provided with two pairs of symmetrical slots, the slots of said pairs being arranged symmetrically with reference to two perpendicular axes drawn on said plate, the slots of each pair being fed by the coaxial cables of the corresponding pair and the plate being provided with a central cross-shaped slot, the arms of which are equal and symmetrical and extend along the bisecting lines of said perpendicular axes, a reflector plate parallel with the slotted plate and lying at a small distance behind the latter and a pair of tubular members interconnecting the two plates near the outer edge of each of the first-mentioned slots. arranged pairwise and into which members the corresponding coaxial cables extend to feed the cooperating slot, the spacing of the tubular members of each pair being substantially equal to the spacing of the plates.

4. An aerial adapted to radiate satisfactorily throughout a very wide range of frequencies, comprising two feeders, a pair of coaxial cables fed by each feeder, a late provided with two pairs of symmetrical slots, the slots of said pairs being arranged symmetrically with reference to two perpendicular axes drawn on said plate, the slots of each pair being fed by the coaxial cables of the corresponding pair and the plate being provided with a central cross-shaped slot, the arms of which are equal and symmetrical and extend along the bisecting lines of said perpendicular axes, a reflector plate lying in parallelism and at a small distance to the rear of the latter, and a mast carrying the two plates horizontally above ground.

5. An aerial adapted to radiate satisfactorily throughout a very wide range of frequencies, comprising two feeders, a pair of coaxial cables fed by each feeder, a plate provided with two pairs of symmetrical slots, the slots of said pairs being arranged symmetrically with reference to two perpendicular axes drawn on said plate, the slots of each pair being fed by the coaxial cables of the corresponding pair and the plate being provided with a central cross-shaped slot, the arms of which are equal and symmetrical and extend along the bisecting lines of said perpendicular axes, a reflector plate lying in parallelism and at a small distance to the rear of the latter, and auxiliary reflector rods extending perpendicularly to each of the perpendicular axes.

6. An aerial adapted to radiate satisfactorily throug out a very wide range of frequencies, comprising two feeders, a pair of coaxial cables fed by each feeder and a square plate provided with two pairs of symmetrical slots, the slots of said pairs being arranged symmetrically with reference to'two perpendicular axes drawn on said plate, the slots of each pair being fed by the coaxial cables of the corresponding pair and the plate being provided with a central cross-shaped slot, the arms of which are equal and symmetrical and extend along the bisecting lines of said perpendicular axes, said slotted plate being folded back across the ends of the arms of the slot, a square reflector plate lying in parallelism with the slotted plate and at a small distance behind the folded parts of the latter and the sides of which are equal to those of the slotted plate, and rods carried by each apex of the reflector plate and the lengths of which are equal to one half the diagonal length of the latter.

References Cited in the file of this patent UNITED STATES PATENTS 2,660,674 Brown Nov. 24, 1953 

